Exhaust silencer for internal combustion engines



J. c. LYTTLE 3,515,242

EXHAUST SILENCER FOR INTERNAL COMBUSTION ENGINES June 2, 1970 Filed Sept. 5, 1959 w m 000 000000000 OQWWV OOOOAWMVOO 0000 0 m OOOOOO OOOOOOO O x r w m m I I f ON A1 u INVENTQR.

JOSH-\H C. LYTTLE ATTORNEYS.

United States Patent O 3,515,242 EXHAUST SILENCER FOR INTERNAL COMBUSTION ENGINES Josiah C. Lyttle, Hatboro, Pa., assignor to Alexander- Tagg Industries, Inc., Warminster, Pa., a corporation of Pennsylvania Filed Sept. 5, 1969, Ser. No. 855,714 Int. Cl. F01n 1/08 U.S. Cl. 181-56 Claims ABSTRACT OF THE DISCLOSURE An exhaust silencer for internal combustion engines is disclosed having a system of expansion/resonator chambers tuned to specific frequencies and so arranged structurally as to avoid adding to the structural length of the silencer. A restriction in the outlet tube causes a reversal of flow into an expansion chamber. Oversized openings or ports are provided in the outlet tube just beyond the restriction to purge the expansion chamber and to keep the back pressure down to acceptable values.

BACKGROUND OF THE INVENTION This invention relates to exhaust silencers for internal combustion engines.

In the design of exhaust silencers, it is often required to construct the silencer unit so that the inlet and outlet connections are in line. Since exhaust gases tend to follow the line of least resistance, problems arise in connection with the provision of the necessary expansion chambers to slow down and cool the gases, and in the provision of resonator chambers and circuitous paths to set up dissonant frequencies to cancel out like incoming frequencies. Back pressure is of prime importance, so that care must be taken not to restrict the flow to abruptly. The flow must be smooth, without creating turbulence.

SUMMARY OF THE INVENTION A principal object of the invention is to provide an exhaust silencer so designed and constructed as to have long service life, improved sound attenuation characteristics, and exhaust back pressures which are minimum or at least within acceptable limits.

Another object is to provide an exhaust silencer which is structurally strong and stable, yet readily manufactured with standard metal working machinery and tools;

It is desirable, but not mandatory, that the unit be of all-metal fusion-welded construction, properly designed to allow expansion and contraction of the metal parts without causing undue distortion in any part of the structure.

The foregoing objects are achieved, in accordance with the present invention, by providing a novel, arrangement of the component parts of the exhaust silencer to provide circuitous routes for the exhaust gases, and to provide resonator chambers so placed, and so calculated as a size, so as to set up dissonant frequencies in the more objectionable octave bands. The arrangement of components in the new exhaust silencer provides ample expansion chambers in the center of the structure to slow down the exhaust gases for the necessary heat dissipation. Near the outlet of the exhaust silencer, the flow of the gases is speeded up by means of a unique arrangement. This speed-up of flow tends to overcome the back pressure created in the expansion chambers and prevents "ice build-up of unburned hydrocarbons within the unit which would tend to cause internal burning or explosion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an exhaust silencer or muffler constructed in accordance with the present invention;

FIG. 2 is a longitudinal sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a transverse sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a transverse sectional view taken along the line 4--4 of FIG.'2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cylindrical shell 1 of sheet metal or other suitable material, and of calculated size, is closed at opposite ends by the headers 16 and 17. Shell 1 will usually have a circular cross section, but this is not essential. The cross-sectional shape may be square, or rectangular, or conical, or other.

A first perforated inlet tube 2, having a diameter sub stantially smaller than the diameter of the shell 1, is supported at the inlet end of the shell 1 by the header 16 and by a bafile 18. Following inlet tube 2, and spaced therefrom by a relatively small distance, is a second perforated inlet tube 22 which is rigidly supported by a combination of component parts including a bafile 19, and a perforated cylindrical shell 6 and bafile 14 which are supported on bathe 18.

At the outlet end of the shell 1 is a perforated outlet tube 3 supported by the header 17 and baffle 20.

The second inlet tube 22 and the outlet tube 3 have the same diameters as the first inlet tube 2, and all three of these tubes are aligned, on the center axis of the shell 1. Shell 6 is of larger diameter, is concentric with tubes 2 and 22, and is coextensive with portions of these two inlet tubes 2 and 22.

The baffle 18, near the inlet end of the shell 1, is located at a selected distance from the header 16 to create a resonator chamber 7 tuned to the 63 hertz and hertz octave bands. It is to be understood that the unit hertz is equivalent to cycles per second.

An expansion/resonator chamber 9 is created in the shell 1 by placement of the bafile 19 so spaced from bafflc 18 that the chamber 9 is tuned to the 250 hertz and 500 hertz octave bands.

An auxiliary expansion/resonator chamber 8 is created within the chamber 9 by the cylindrical perforated shell 6 and by the baflies 14 and 18. These bafllles are so spaced that auxiliary chamber 8 is tuned to the 1,000 hertz octave band.

A restrictor 4 is placed within the second inlet tube 22, as shown.

An expansion/resonator chamber 10 is created in the shell 1 by placement of the baffle 20 at a calculated position so spaced from the baffle 19 that the chamber 10 is tuned broadly to the 125 hertz through 1,000 hertz octave bands. Chamber 10 carries a percentage of the exhaust gases which have passed through the opening in the tube restrictor 4 in the inlet tube 22.

As seen in FIGS. 2 and 4, baffle 20 is provided with openings 12 of calculated size to allow passage between the broad-band chamber 10 and the chamber 11. Four such openings 12 are shown in the illustrated embodiment. Chamber 11 is created by the baffle 20 and header 17 and is of a size to be tuned to the 2,000 hertz and 4,000 hertz octave bands.

In operation, the exhaust gases from the internal combustion engine enter the silencer at the inlet end by passing into the perforated inlet tube 2. Some of the gases pass through the perforations 13 in tube 2 and enter chamber 7 which is tuned to the 63 hertz and 125 hertz octave bands.

It is to be understood that the sound frequency or frequencies to which a particular chamber is tuned is a function of the length, diameter and volume of the chamber.

It is also to be understood that the purpose of providing resonator chambers is to establish standing waves at selected frequencies to oppose and cancel out incoming gases at like frequency or frequencies. Sound frequencies in the 125 hertz octave band are, for example, highly objectionable in that the human ear is very sensitive thereto. Thus, it is a purpose and function of the expansion/ resonator chamber 7 to establish standing waves which are 180 out of phase with subsequent incoming waves in the 63 and 125 hertz octave bands, and to cancel out and attenuate these objectionable sound waves.

Returning now to the operation of the exhaust silencer of the present application, it has been just explained that exhaust gases entering tube 2 and having frequencies in the 63 and 125 hertz octave bands are substantially cancelled out by the waves established in the expansion/ resonator chamber 7. Gases which flow inside tube 2 are impeded by the restrictor 4 and expand, through the space 122 between inlet tubes 2 and 22, and also through the perforations 13 and 33 in tubes 2 and 22, into the expansion/resonator chamber 8 which is tuned to the 1,000 hertz octave band. Thus, chamber 8 is effective to cancel out incoming gases having a frequency in the 1,000 octave band. Some of the gases in chamber 8 pass through the perforations 23 in the cylindrical wall of chamber 8 and enter into expansion/resonator chamber 9 which is tuned to the 250 and 500 hertz octave bands. Thus, incoming gases in the 250 and 500 hertz bands are largely dissipated by the action of chamber 9.

The gases which enter chamber 9 are blocked by the baffle 19 and are forced to re-enter the second inlet tube 2 through perforations 33 on the outlet side of restrictor 4. The combination just described of restriction (by restrictor 4) in tube 2, expansion into chamber 8, and resonance in chamber 8, combined with a repeat of expansion and resonance in chamber 9 creates dissonance to reduce substantially loudness in the 250 hertz through the 1,000 hertz octave bands.

A certain percentage of the exhaust gas flow in the inlet tube 2 passes freely through the opening in the tube restrictor 4. This flow carries with it all sound frequencies within the more audible eight octave bands (63, 125, 250, 500, 1,000, 2,000, 4,000 and 8,000 hertz) If allowed to continue, this noise will carry on to the outside atmosphere. However, in the exhaust silencer of the present application, a restrictor is placed in outlet tube 3. Restrictor 5 causes a 180 reversal of the flow, as shown by the arrows, into expansion chamber 10, which, as previously indicated, is tuned broadly to the 125 through 1,000 hertz octave bands. This reversal of flow is out of phase with the incoming gases and sets up a dissonance to cancel out or counteract the sound frequencies carried by the free flow through tube 2. However, if not corrected, this reversal of flow just described would create an excessive back pressure.

To avoid the excessive back (which otherwise would be created by the reverse flow at outlet restrictor 5) two (or more) large openings 15 are provided in the cylindrical wall of outlet tube 3 just beyond the restrictor 5. Openings 15 are so strategically placed, in relation to restrictor 5, as to create a low pressure which tends to purge broadly-tuned expansion chamber 10 and thus keep the back pressure within acceptable limits without interfering with sound attenuation.

Some of the gases in chamber 10 pass through openings 12 in the bafile 20. Baffle 20 together with header 17 define the expansion/resonator chamber 11 which is tuned to the 2,000 hertz and 4,000 hertz octave bands. The gases going into the chamber 11 re-enter the outlet tube 3 through the openings 43.

It will be seen from the foregoing description that the gases which pass from the silencer through the mouth of outlet tube 3 are substantially free of sounds of substantial amplitude in the 63 through 4,000 hertz bands. Thus, sounds in the frequency bands to which the human ear is most sensitive have been dissipated and largely removed by the silencer of the application.

It will be understood that the particular overall dimensions for the exhaust silencer, and the particular dimensions for the various resonator chambers established therein, are related to the cubic displacement of the particular internal combustion engine to be exhausted and the cubic-feet-per-minute flow of exhaust gases from the engine. The cubic displacement of the engine and the cubicfeet-per-minute flow of the exhaust gases also determine the amount of openings to be created by the perforations in the various tubular parts and the specific dimensions of the low pressure feature involving outlet restrictor 5 and openings 15.

The operation of the exhaust silencer of the present application may be summarized as follows: Exhaust gases from the internal combustion engine of the motor truck, bus, tractor or other vehicle are in pulsating form with alternating regions of high and low pressure. The frequency spectrum of the gas pulses is complex, but certain frequencies predominate. These depend upon engine design, speed of operation and other factors. Upon entering the inlet tube 2, the gases during a high pressure interval expand through the openings 13 into the chamber 7, tuned to 63 and hertz octave bands. During the low pressure period, at the 63 and 125 hertz frequencies, gases from chamber 7 return through the openings 13 into the tube 2. This action substantially smooths out and thus largely eliminates the 63 and 12S hertz pulses from the gases which pass onward through the silencer. Restrictor 4 impedes the onward flow, and causes the high pressure regions of gas to expand through the space 122, and through the openings in the tubes 2 and 22, into the chamber 8, tuned to 1,000 hertz octave band. During the low pressure periods at 1,000 hertz, gases from chamber 8 return to the tubes 2 and 22. Gages in chamber 8 also expand through openings 23 into chamber '8, tuned to the 250 and 500 hertz octave bands. During the low pressure intervals at these frequencies, gases from chamber 9 expand through holes 33 back into tube 22 on the output side of restrictor 4, thereby smoothing out and substantially eliminating sound pulses at the 250 and 500 hertz octave bands. As the flow continues onward through tube 3 the restrictor 5 is encountered which causes a reversal of flow of some of the gases and expansion through the holes in the wall of tube 3 into chamber 10 broadly tuned to the 125 through 1,000 hertz bands. Except for the fact that chamber 10 is broadly tuned, the expansion/ resonator action of chamber 10 is generally similar to that of the other chambers, as already described, and further smoothing out of the pulsations in the gas flow in tube 3 is eifected. To avoid undesirable back pressure in chamber 10, two large openings 15 are provided in the wall of tube 3 on the outlet side of the restrictor 5. I have found that this allows the gases in chamber 10 to flow rapidly into the discharge end of tube 5 and avoids what would otherwise be an undesirably high back pressure in chamber 10 without however destroying the smoothing action of chamber 10. Some gas from chamber 10 also expands through openings 12 in baffle 20 into chamber 11. Gas also expands through the openings 43 in tube 5 into chamber 11. Chamber 11 is tuned to the 2,000 and 4,000 hertz octave bands, and the effect of chamber 11 is to smooth out and hence substantially eliminate pulses at these frequencies from the gases finally discharged from the silencer. Thus, the exhaust gas discharged from the silencer to the atmosphere has had its pulsating character largely removed by the silencer just described.

What is claimed is:

1. An exhaust silencer for internal combustion engines, said silencer comprising:

(a) an elongated tubular shell having headers at each end thereof;

(b) a first perforated inlet tube supported by the inlet header and by a first transverse baflle;

(c) a second perforated inlet tube spaced longitudinally from said first inlet tube and supported within said shell by means including a second tranverse baflie;

(d) a perforated auxiliary tube of larger diameter than said first and second inlet tubes supported within said shell in a position surrounding adjacent portions of said first and second inlet tubes;

(e) said auxiliary tube being supported at one end by said first bafile and at the other end by a third transverse batfie;

(f) said-third transverse bafile being supported on said second inlet tube and having a diameter corresponding to the diameter of said auxiliary tube;

(g) a perforated outlet tube supported at the outlet end of said shell by the outlet header and by a fourth transverse bafile within said shell;

(11) said inlet header and first baffle forming a first resonator chamber tuned to first frequencies;

(i) said first and second baffles forming a second resonator chamber tuned to second frequencies higher than the first frequencies;

(j) said auxiliary tube forming a third resonator chamber tuned to third frequencies higher than said first and second frequencies;

(k) said second and fourth baflies forming a fourth resonator chamber broadly tuned to a range of frequencies including said first, second and third frequencies;

(l) a first restrictor within said second inlet tube to force some of the exhaust gases into said third and second resonator chambers;

(m) a second restrictor within said outlet tube inward of the location of said fourth barrier for forcing gases into said fourth resonator chamber;

(n) aperture means of sufiiciently large size in the wall of said outlet tube between said second restric tor and said fourth baflle to allow fast passage of gases therethrough into said outlet tube thereby to reduce substantially the back pressure in said fourth resonator chamber.

2. An exhaust silencer according to claim 1 characterized in that said fourth transverse baflle and said outlet header define a fifth resonator chamber tuned to frequencies higher than said first, second and third frequencies.

3. An exhaust silencer according to claim 2 characterized in that:

(a) said first resonator chamber is tuned to 63 and 125 hertz octave bands;

(b) said second resonator chamber is tuned to 250 and 500 hertz octave bands;

(c) said third resonator chamber is tuned to 1,000

hertz octave bands;

(d) said fourth resonator chamber is broadly tuned to frequencies between 125 through 1,000 hertz octave bands.

4. An exhaust silencer according to claim 3 characterized in that said fifth resonator chamber is tuned to 2,000 and 4,000 hertz octave bands.

5. An exhaust silencer according to claim 1 characterized in that:

(a) said shell is circular in cross section;

(b) said inlet and outlet tubes are circular in cross section, and are of equal diameters;

(c) said auxiliary pipe is circular in cross section;

(d) said transverse bafiles are annular.

6. An exhaust silencer comprising:

(a) an elongated tubular shell closed at both inlet and outlet ends by apertured headers;

(b) an inlet tube in the aperture of the inlet header;

(c) an outlet tube in the aperture of the outlet header;

(d) transverse bafi'les at selected locations within said shell and surrounding said inlet and outlet tubes for forming a plurality of resonator chambers within said shell tuned to different frequencies in the audible range;

(e) a restrictor in the outlet tube for causing a reverse flow of gases to cancel forward flow of gases and to force gases into one of said resonator chambers;

(f) aperture means in the wall of said outlet tube on the outlet side of said restrictor for purging said lastmentioned resonator chamber to reduce the back pressure therein.

7. An exhaust silencer according to claim 6 characterized in that a restrictor is also placed in said inlet tube for forcing gases into other of said resonator chambers for establishing waves therein at selected frequencies for opposing and dissipating incoming wave energy at said selected frequencies.

8. An exhaust silencer according to claim 7 characterized in that one of said other resonator chambers into which gases are to be forced by the restrictor in said inlet tube is an auxiliary chamber having a diameter larger than said inlet tube and mounted concentrically thereon.

9. An exhaust silencer according to claim 8 characterized in that said inlet tube is comprised of two sections spaced axially apart, and in that said auxiliary resonator tube is concentric to, and coextensive with, adjacent portions of both sections of said inlet tube.

10. An exhaust silencer for internal combustion engines, said silencer comprising:

(a) an elongated tubular shell;

(b) a perforated inlet tube of diameter smaller than said shell;

(0) means including an inlet header and a first transverse baflle forming therebetween a first resonator chamber tuned to specific frequencies in the audible range;

(d) a perforated auxiliary tube within said shell of larger diameter than and concentric with said inlet tube and coextensive with a portion of said inlet tube and closed at each end and forming an auxiliary resonator chamber tuned to other specific frequencies in the audible range;

(e) transverse restrictor means within said inlet tube for passing a portion of exhaust gases and for causing another portion of said gases to pass through the perforations in said inlet tube into said auxiliary resonator chamber;

(f) a second transverse bafile supporting the inner end of said inlet tube and forming with said first transverse barrier a second resonator chamber tuned to still other specific freqeuncies in the audible range, a portion of said second resonator chamber being occupied by said auxiliary resonator chamber;

(g) a perforated outlet tube of diameter smaller than said shell;

(b) means including an outlet header and a third transverse bafile for forming between said second and third transverse bafiles a third resonator chamber tuned broadly to frequencies in the audible range;

(i) said fourth bafile together with the outlet header forming therebetween a fourth resonator chamber tuned to frequencies in the audible range higher than the frequencies to which said first, second or third References Cited chambers are tuned; (j) a restrictor in said inlet tube for forcing gases to UNITED STATES PATENTS flow into said auxiliary resonator chamber and 2,150,811 3/1939 Starkweather et 181-55 through said auxiliary resonator chamber into said 5 2,220,866 11/1940 Jensen et second resonator chamber; FOREIGN PATENTS (k) a second restrictor in said outlet tube for causing reversal of gas flow and for forcing gases into said third broadly tuned resonator chamber;

(1) openings of relatively large size in the wall of said 10 outlet tube on the outlet side of said second restrictor I for establishing a low pressure condition for purging ROBERT WARD Pnmdry Exammel said third resonator chamber, thereby to avoid high U 5 cl XR back pressures Which would otherwise be created by said reversal of gas flow. 5 63 1,189,372 3/1959 France.

803,452 4/ 1951 Germany. 405,512 8/1943 Italy. 

